Microwave apparatus for the processing or measurement of sheet materials



J. BILBRouGl-l 3,488,858 MICROWAVE APPARATUS FOR THE PROCESSING OR Jan.l13, 1970 MEASUREMENT OF SHEET MATERIALS 4 Sheets-Sheet l Filed Jan. 29,1968 Jan- 13, 1970 J. BILBROUGH 3,488,858

' MICROWAVE APPARATUS FOR THE PROCESSING OR l MEASUREMENT OF SHEETMATERIALS Filed Jan. 29, 1968 4 Sheets-Sheet 2 Jan. 13, 1970 J.MICROWAVE APPAR BILBROUGH ATUS FOR THE PROCESSING OR MEASUREMENT OFSHEET MATERIALS Filed Jan. 29, 1968 f lvl/ll Il' N f mi Jan. 13, 1970 J.BILBROUGH 3,488,858

MICROWAVE APPARATUS FOR THE PROCESSING OR MEASUREMENT OF SHEET MATERIALSFiled Jan. 29, 1968 4 Sheets-Sheet 4 y TW :Lu-vereren JACK. BILB Rox/@HAvvonuevs United States Patent O 3,488,858 MICROWAVE APPARATUS FOR THEPROCESSING OR MEASUREMENT OF SHEET MATERIALS Jack Bilbrough,Newcastle-upon-Tyne, England, assignor to The Rank Organisation Limited,London, England, a company of Great Britain and Northern Ireland j FiledJan. 29, 1968, Ser. No.'701,139 Claims priority, application GreatBritain, Jan. 30, 1967,

4,508/67; May 9, 1967, 21,542/ 67 Int. Cl. F26b 5/02 U.S. Cl. 34-1 5Claims ABSTRACT F THE DISCLOSURE The specification describes forms ofhollow waveguides for microwave propagation which are slotted to allowthe passage of a sheet or web of material through the waveguide interiorso that the microwave power in the waveguide can be employed to controland/0r measure the moisture content of the material as it passes throughthe slots. The waveguides are characterized by the provision of meansfor the ejection of a pressure gas flow at or adjacent the edges of theslots to provide a cushion effec-t protecting the surface of thematerial `and also to limit the danger of foreign matter carried by thematerial falling into the waveguide. The cushioning tlow may be fromwithin the waveguide, preferably through slots or through a permeablescreen, or from conduits that are outside the microwave path. Thepressure gas used may be arranged to perform a process operation uponthe material.

This invention relates to microwave apparatus for use in the control ofthe moisture content of sheet materials and/or for the measurement ofsuch moisture content.

It has been proposed to use -for the measurement of moisture content ofsheet materials, microwave apparatus in which a hollow waveguide sectionhas slots along opposed Walls, the plane of the slots being parallel tothe E plane of the microwaves directed through the waveguide and thesheet material being in the form of a continuous web traversing thewaveguide through the slots. The attenuation of microwave energydirected through the slotted `waveguide is then indicative of themoisture content of the web.

Such an arrangement can present difficulties due to foreign bodiescarried by the travelling web falling into the hollow waveguide sectionso causing uncontrolled variations in the measurement signals from thewaveguide and also, where the sheet material is fragile or otherwiseliable to damage by contact or rubbing, tissue papers and photographiciilm are Itwo examples, the waveguide sections may harm the materialsince the free space that can be left at the slots is limited.

According to the present invention, there is provided a hollow waveguidefor use in the control and/ or measurement of the moisture content of asheet material and having opposed slotted walls of which the slotsdefine a planar region for the passage of the sheet material yacross theinterior of the waveguide, means being provided for the ejection of apressure gas flow at or adjacent the edges of the slots at least at oneface of said planar region. The pressure medium may be ejected throughconduit means outside the interior or microwave path of the waveguide,such means opening at or adjacent the slots or, alternatively, thei/'aveguide can itself form a conduit for the pressure meium.

In the latter case, the gas can be injected into the waveguide throughone or more relatively large entry conduits provided with meanspreventing the propagation of microwave energy through said conduit orconduits or it can be ICC injected through a series of small aperturesarranged to be opaque to the microwave energy by virtue of their sizeand positions.

It' the pressure gas ow is intended to maintain the sheet material outof contact with the edges of the slot, it will usually be required toprovide flow injection means at both faces of said planar region.

'Particularly if the pressure ow issues from the Waveguide itself, eachor either half of the waveguide at the dividing planar region may beprovided with a screening sheet pervious to said gas flow and extendingacross the edges of the slots to give a more even distribution of theflow along the length of -the waveguide. Such `a sheet may be of apreferably woven fabric or of a perforate material and in the lattercase the perforations can be so distributed as to vary the rates of gasflow through the screening sheet at different regions thereof, e.g.concentrating the flow at particular regions of the edges of the slots.

` Various embodiments of the invention will now be described withreference to the drawings wherein:

FIGS. 1 to 3 are mutually perpendicular sectional views of one form ofwaveguide according to the invention,

FIG. 4 shows in front elevation a further embodiment of the invention,

FIG. 5 is a sectional view on the lines V--V in FIG. 4,

FIG. 6 is a perspective view of one part of a further form of waveguideaccording to the invention,

FIGS. 7 and 8 are mutually perpendicular sectional views of thewaveguide of FIG. 6,

FIG. 9 illustrates a modified version of the waveguide of FIGS. 1 to 3,and

FIG. 10 illustrates a further modification of a waveguide according tothe invention. f

Referring more particularly to FIGS. 1 to 3 of the drawings, thewaveguide 2 is U-shaped and is formed in two halves in a pair ofparallel plates 4 separated by a central gap or slot 6 in the plane ofthe U that allows a web W to be passed between the plates. At the endsof the U-shape are perpendicularly directed inlet and outlet sections10, 12 for the connection of the waveguide to a microwave circuit.

At the mutually remote faces of the plates 4 are respective manifolds 14having pressure air inlet `pipes 16, a series of small, spaced apertures18 along the length of the U-shaped portions connecting the manifolds tothe interior of the waveguide. At their adjacent faces, the plates haverespective screens of fabric or perforate sheets 20 laid over them andheld fixed by securing strips 22. These sheets prevent the passage ofsolid matter into the interior of the opposed portions of the waveguidebut allow air from the manifold to pass in a relatively evenlydistributed flow through the faces to the gap or slot `6 so that the webW is cushioned -by the air flow and can be kept out of contact with thewaveguide structure. If itis necessary to close the paths through theinlet and outlet waveguide sections 10, 12 to the air flow seals can beprovided, such as the polythene sheet 24 illustrated, which will betransparent to micro- Wave radiation although impermeable to the airflow. Escape of microwave energy -through the apertures 18 is precludedby selecting the size and disposition of the apertures so that they areopaque to these energy frequencies and do not cause interference withthe signals generated.

In the construction shown in FIGS. 4 and 5 the slotted waveguide isformed by a pair of opposed plates 28 of channel form cross-section, theside limbs of the two channels defining the slots 30 betwe'en them, andthe interiors of the waveguide portions are connected to oppositelyoffset or cranked inlet and outlet waveguide sections 32, 34, onesection being secured to each of the plates 28. Respective conduits 36,38 now lead pressure air directly into the microwave path at thesections 32,

3 34 and to prevent the escape of microwave energy through the conduits,reflecting posts 40 or resonant sections may be incorporated adjacenttheir junctions with the waveguide sections.

Similarly to the' previous example, FIG. 4 shows a polythene sheet airseal 42 inserted at the junction between the waveguide inlet section 32and the preceding waveguide portion and a similar seal will also beprovided at the end of the exit section 34. FIGS. 4 and 5 also show apervious sheet 44 extending between the edges of the slots 30 at eachadjacent face of the plates 28, the sheets being held in position bysecuring strips 46.

In FIGS. 6 to 8, sections 50 of the slotte'd waveguide are now providedintegrally with air inlet manifolds 52, each section being formed from ahollow E-section tube. The waveguide `formed by the parallel recesses ofthe tube sections may be U-shaped as in the rst-illustrated example orthese recesses may provide a pair of alternative paths in parallel. Theair escapes from the manifolds 52 at transverse slots 54 at the opposedfaces 5'6 of the slots and at the remote opposed faces 58 of thewaveguide interior. By giving the slots a suitable distribution, it isnot necessary to provide a pervious sheet to distribute the air flowalong the waveguide. An air seal 60 is again provided at each adjoiningwaveguide section.

In this example it may be possible to dispense with the slots in theremote faces 58 so that air is not blown into the path of the microwaveradiation; this arrangement is shown in FIG. 9 where air from themanifolds 14 is ejected through apertures 62 spaced from the microwavetransmission path of the waveguide interior. As the air then does notneed to flow through the waveguide interior it would be possible to llthese interior spaces to the level of the faces of the slots with asolid dielectric material 64 so closing olf the waveguide interior tothe ingress of air or foreign matter.

If the pressure air is not required to ow through any part of themicrowave energy path, it is possible to provide discrete means attachedto or suspended adjacent to the slots of the waveguide to eject thepressure flow at or adjacent the edges of the slots. In many instancesthe provision of a gas flow at the peripheral slots of the waveguide mayprovide a sufficient cushioning effect, such an arrangement being shownin FIG. where tubes 68 are attached to the sides of the waveguide toextend along said sides, and have a series of apertures 69 along theirlength for the pressure gas emission.

It will be appreciated that the present invention is applicable toslotted waveguides of very diverse form. For example, the U-shape shownin FIG. 1 can be elaborated into a convoluted or serpentine form.Furthermore the gas flow may be provided on one side of the sheet onlywhere, for example, it is only required to provide a supporting cushionfrom below or where one face only of the sheet has a coating which mustbe protected from rubbing damage.

In use of the invention, the pressure gas employed need not be air butcan be chosen with regard to the particular sheet material being passedthrough the waveguide and the gas can be iirst ltered, dried, heated orcooled as required and may even be so chosen as to itself effect aprocess step, e.g. drying, heating or a chemical reaction, on thematerial,

It will be appreciated that the microwave' circuits with which awaveguide according to the invention can be employed, whether for thecontrol or the measurement of the moisture content of the sheet materialbeing processed may take any conventional form and therefore need nodescription here.

What I claim and desire to protect by Letters Patent is:

1. A hollow waveguide for use in the control and/or measurement of themoisture content of a sheet material comprising, in combination, a pairof opposed walls and respective slots in said walls, the edges of theslots defining a planar region across the width of the waveguide betweensaid walls for the passage of a sheet material through the waveguideinterior, a gas entry passage coextending with the waveguide, gasejection means comprising a series of apertures along the length of thepassage to open at or adjacent the edges of the slots at least at oneface of said planar region outside the boundaries of the associatedmicrowave transmission path of the waveguide to provide a gas flowbetween said sheet material and the slot edges of at least one face.

2. A hollow waveguide according to claim 5 further including a gas entrymanifold co-extending with the waveguide, said ejection means comprisinga series of apertures along the length of the manifold wherein themanifold apertures open in the faces of the slots outside the boundariesof the associated microwave transmission path.

3. A hollow waveguide according to claim 1 wherein the microwave pathfrom the opposed faces of said planar region is filled with a dielectrictransparent to microwave transmission.

-4. A hollow waveguide according to claim 1 wherein said gas is selectedor treated to perform a process operation upon the sheet material.

5. A hollow waveguide for use in the control and/ or measurement of themoisture content of a sheet material comprising, in combination, a pairof opposed walls and respective slots in said walls, the edges of theslots defining a planar region across the width of the waveguide betweensaid walls for the passage of a sheet material through the waveguideinterior, gas ejection means being arranged at or adjacent the edges ofthe slotsat least at one face of saidy planar region and outside themicrowave path through the waveguide, and said path, from the planarregion defined by the opposed faces, being filled with a dielectrictransparent to microwave transmission.

References Cited UNITED STATES PATENTS 3,263,052 7/1966 Jepson et al.2l9-10.55

FOREIGN PATENTS 1,048,3 17 11/1966 Great Britain.

1,050,493 12/ 1966 Great Britain.

1,014,117 12/1965 Great Britain.

KENNETH W. SPRAGUE, Primary Examiner U-S, Cl.- X.R. 13.19-10.55

